Generally speaking (and this may differ across states) a forensic psychologist is defined by the work they do. All independently practicing clinical psychologists must have a doctorate in psychology, 3000 hours of supervised experience & 2 board exams in order to practice independently. Although you can do coursework in forensic psychology and some internships are forensic placements, the primary qualification, in California is a license in psychology and a good understanding of the laws and regulations governing this area. The California psychology license is a general license and (with the exception of neuropsychology) and the clinician is left to determine their scope of practice given their training and expertise. A forensic psychologist is also different from an expert witness, which is a designation given by the court and not always tied to academic qualifications.